SQL Server - How to set the Month and Year in Table Column with Trigger????

I want to write one trigger in which I want to set one column of the Table in the format of  month and year like         'MMM-YYYY' i.e. Nov-2013 after updating the other column of the table..

Problem is not the updating second column problem is set the month and year in the first column.  So what I have to write in my trigger?